The dose and X-ray energy response of LiF:Mg,Cu,P and CaSO4:Dy thermoluminescent foils

• Development of a novel system using a planar 2D thermoluminescent (TL) reader.
• The system allows 2-D dose distributions to be obtained in the form of digital images.
• X-ray energy and dose response of foils with LiF:Mg,Cu,P or CaSO4:Dy as TL phosphors.
• Applicability of the 2D TL system in dosimetry of diagnostic X-rays beams is discussed.

Within a systematic study of a novel system enabling 2D readout of TL foils, the X-ray energy and dose response was investigated in TL foils containing LiF:Mg,Cu,P (MCP-N) or CaSO4:Dy as activators. Foils were exposed to broad X-ray beams of mean energies ranging between 45 keV and 208 keV (ISO 4037 standard), with reference to 662 keV 137Cs gamma rays. The MCP-N foils, of about 380 nm emission wavelength, show a flat X-ray energy response, but low sensitivity. Due to poor TL light detection efficiency of the CCD (charge-coupled device) camera over this range of wavelengths, only doses exceeding 500 mGy can be reliably measured. In the case of CaSO4:Dy foils, their TL light emitted around 450 nm wavelengths is registered by the CCD camera with no loss of efficiency, enabling X-ray doses as low as 100 mGy to be evaluated. Unlike that of MCP-N, the dose response of CaSO4:Dy foils is highly supralinear. Nevertheless, within experimental conditions applied in this study, the 2D-TL technique may be applied to determine Entrance Surface Dose or Maximum Skin Dose in radiology. The more sensitive CaSO4:Dy foils could be used only in a well-specified radiation field (e.g., in mammography) or in qualitative dose mapping.